Digital video signals such as, for example, digital television channels are typical compressed (a.k.a. encoded) (e.g. in accordance with International Telecommunications Union recommendation (ITU-T) H.264 Advanced Video Coding for Generic Audiovisual Services) before transmission in order to reduce the transmission bandwidth requirement. Both intra-frame and inter-frame compression techniques can be used. An intra-coded frame is a fully-specified frame (a.k.a. I-frame) that does not need to refer to any other frame to be decoded. An inter-coded frame can be in the form of a P-frame that only contains information relating to changes from a preceding frame, or in the form of a B-frame that contains information relating to differences between the current frame and both the preceding and the following frames. P-frames can only be decoded in the context of a preceding frame while B-frames can only be decoded in the context of a preceding frame and a following frame. I-frames are the least compressed while P-frames and B-frames are more compressed.
A typical coded (i.e. compressed) video signal (i.e. stream) comprises I-frames spaced apart at intervals in time with a series of P- or B-frames in between I-frames. The use of both I-frames and P- or B-frames permits for greater compression than the use of I-frames alone.
Generally the greater the time interval between I-frames the greater the compression of video signal, but also the greater the delay before decoding of the video stream can start when switching to the video stream. When switching to a compressed video streams, decoding of the stream cannot start until an I-frame is received. A point in the video stream where decoding can begin is also referred to as a random access point (RAP). The time lapse between when a switch is made to a video stream (e.g. Internet Protocol television (IPTV) channel) and when decoding can begin is referred to as a join delay.
Various solutions have been proposed in order to minimize the join delay. These include the solution described in United States Patent Publication No. 2007/0250890 A1 the entirety of which is incorporated herein by reference. The present invention improves upon the solution described in the incorporated reference which, for example, does not provide a mechanism for abstracting a heterogeneous set of Video-on-Demand (VOD) servers for use by a single middleware client.